Volume 91, Issue 3, 01 February 2002
Index of content:
- APPLIED BIOPHYSICS (PACS 87)
91(2002); http://dx.doi.org/10.1063/1.1428801View Description Hide Description
In this article, we propose a method for three-dimensional optical trapping of metallic Mie particles using an obstructed laser beam. It is found from the ray-optics model that Mie gold,silver, and copper particles can be trapped against gravity in the focal region of a high numerical-aperture objective illuminated by a centrally obstructed Gaussian -mode) beam. The axial trapping force of the three types of metallic particles is maximized in the near-infrared wavelength region. The maximum axial trapping efficiency increases with the size of the center obstruction and the aperture angle of an objective. Axial trapping force on Mie metallic particles is enhanced by a factor of two if an obstructed doughnut -mode) beam is employed. The experimental condition for achieving three-dimensional trapping is also discussed.
91(2002); http://dx.doi.org/10.1063/1.1426244View Description Hide Description
X-ray fluorescence spectroscopy and Fe K-edge x-rayabsorption near-edge structure spectroscopy were performed on postmortem human tissues containing nerve cells in order to investigate distributions and chemical states of iron. Specimens used in this study were obtained from the substantia nigra of a patient with Parkinsonism-dementia complex (PDC) of Guam and a control subject. Iron concentration was observed in the neuromelanin granules and in one of the glial cells surrounding the neuromelanin granules of the PDC patient. Iron was also detected in melanized neurons of the control subject. Chemical state imaging which separates and in iron compounds showed that the glial cell of the PDC patient has a higher concentration of Iron contained in the neuromelanin granules of the PDC patient was mixed states of and